Process control systems, like those used in chemical, petroleum or other processes, typically include a centralized process controller communicatively coupled to at least one host or operator workstation and to one or more field devices via analog, digital or combined analog/digital buses. The field devices, which may be, for example, valves, valve positioners, switches and transmitters (e.g., temperature, pressure and flow rate sensors), perform functions within the process such as opening or closing valves and measuring process parameters. The process controller receives signals indicative of process measurements made by the field devices and/or other information pertaining to the field devices, uses this information to implement a control routine and then generates control signals which are sent over the buses to the field devices to control the operation of the process. Information from the field devices and the controllers is typically made available to one or more applications executed by the operator workstation to enable an operator to perform any desired function with respect to the process, such as viewing the current state of the process, modifying the operation of the process, et cetera.
In the past, conventional field devices were used to send and receive analog (e.g., 4 to 20 mA) signals to and from the process controller via an analog bus or analog lines. These 4-20 mA signals were limited in nature in that they were indicative of measurements made by the device or control signals generated by the controller required to control the operation of the device. However, in the past decade or so, smart field devices including a microprocessor and a memory have become prevalent in the process control industry. In addition to performing a primary function within the process, smart field devices store data pertaining to the device, communicate with the controller and/or other devices in a digital or combined digital and analog format, and perform secondary tasks such as self-calibration, identification, diagnostics, et cetera. A number of standard and open smart communication protocols such as the HART®, Profibus®, World FIP®, Device-Net®, and CAN protocols, have been developed to enable smart field devices made by different manufacturers to be used together within the same process control network.
There has been a move within the process control industry to decentralize process control functions. For example, the all-digital, two-wire bus protocol promulgated by the Fieldbus foundation known as the FOUNDATION™ Fieldbus (hereinafter “Fieldbus”) protocol uses function blocks located in different field devices to perform control operations previously performed within a centralized controller. In particular, each Fieldbus field device is capable of including and executing one or more function blocks, each of which receives inputs from and/or provides outputs to other function blocks (either within the same device or within different devices), and performs some process control operation, such as measuring or detecting a process parameter, controlling a device or performing a control operation, such as implementing a proportional-derivative-integral (PID) control routine. The different function blocks within a process control system are configured to communicate with each other (e.g., over a bus) to form one or more process control loops, the individual operations of which are spread throughout the process and are, thus, decentralized.
With the advent of smart field devices, it is more important than ever to be able to quickly diagnose and correct problems that occur within a process control system, as the failure to detect and correct poorly performing loops and devices leads to sub-optimal performance of the process, which can be costly in terms of the both the quality and the quantity of product being produced. Many smart devices currently include self-diagnostic and/or calibration routines that can be used to detect and correct problems within the field device. Unfortunately, the wealth of new diagnostics and/or calibration abilities of smart field devices can, in some instances, generate problems. For example, a given H1 Fieldbus loop can couple to a number of FOUNDATION™ Fieldbus-compatible field devices. Each such field device may be generating a wealth of digital information, including process variable information, or receiving control information from a controller. Moreover, each field device may also be generating diagnostic information as well as any other suitable digital information. The result is that the maximum bandwidth of the H1 Fieldbus network (31.25 kbps) may become overwhelmed by the data communication needs of multiple smart field devices on a given H1 Fieldbus network.
Providing an adaptation to the H1 FOUNDATION™ Fieldbus network that allows higher communication rates over the network, thereby increasing the useable bandwidth of the H1 Fieldbus network, would be highly beneficial.